From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9CBC4C56202 for ; Tue, 17 Nov 2020 11:07:23 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 321FE207D3 for ; Tue, 17 Nov 2020 11:07:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="08pH9JSg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 321FE207D3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=/n4iJqK9VoSkYpPprieZEPauYsvO9860dA1VG7BSTik=; b=08pH9JSgg/+NugjD7R5JP2Nyk Am7VI31NctBInne13nb8PSatbW/zx0dLbe+d9l33hpFkCLh/y6Ue6yakOThIbZx1JRw13YItHr3G2 +VG2qmoKqjnaZZr8SvdOKeYHlENODWUSVPyoUyMHdTtuPWbyxJ8hHx5LLllFqKRpq2mXNQ7CZWEq0 w5CaFKvHSWfEHrlphfm6g0QmzNHwp/3MQ7SNx6hHciW+waam2+qU4AsMRBbV/DtGF0z199eAXxrBp QjX2M2DZvOIgTbWzI1PJbVhngV1ASOsEvQMrWZdtbZ8g5nt+6xILjZ2x1IqWDXYZeSslaBKR57iJp r65YvVSoQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1keyoq-0001cB-05; Tue, 17 Nov 2020 11:06:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1keygE-0005rr-HQ for linux-arm-kernel@lists.infradead.org; Tue, 17 Nov 2020 10:57:48 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6E49CD6E; Tue, 17 Nov 2020 02:57:44 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.27.161]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 01D1E3F718; Tue, 17 Nov 2020 02:57:42 -0800 (PST) Date: Tue, 17 Nov 2020 10:57:40 +0000 From: Mark Rutland To: Catalin Marinas Subject: Re: [PATCHv4 14/17] arm64: uaccess: remove set_fs() Message-ID: <20201117105740.GB73209@C02TD0UTHF1T.local> References: <20201113124937.20574-1-mark.rutland@arm.com> <20201113124937.20574-15-mark.rutland@arm.com> <20201117104454.GA73209@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201117_055746_726176_5064FE76 X-CRM114-Status: GOOD ( 24.52 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: james.morse@arm.com, will@kernel.org, hch@lst.de, linux-arm-kernel@lists.infradead.org, robin.murphy@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 17, 2020 at 10:54:18AM +0000, Catalin Marinas wrote: > On Tue, Nov 17, 2020 at 10:44:54AM +0000, Mark Rutland wrote: > > On Mon, Nov 16, 2020 at 05:40:48PM +0000, Catalin Marinas wrote: > > > On Fri, Nov 13, 2020 at 12:49:34PM +0000, Mark Rutland wrote: > > > > We no longer need to flip UAO to access kernel memory under KERNEL_DS, > > > > and head.S unconditionally clears UAO for all kernel configurations via > > > > an ERET in init_kernel_el. Thus, we don't need to dynamically flip UAO, > > > > nor do we need to context-switch it. However, we do need to clear UAO > > > > (and set PAN) during SDEI entry. > > > > > > If the kernel never sets the UAO bit, why do we need to clear it during > > > SDEI entry? > > > > The fear was taking an SDEI event from a VM which had UAO set, with the > > SDEI FW not clearing UAO. > > > > That might not happen in practice because while the spec implies that > > could happen, TF-A currently generates a new PSTATE from scratch, and > > going forward the spec will be aligned with regular exception entry > > rules for PSTATE (so UAO will be cleared automatically). > > Does this requirement apply retrospectively or it only for the future > SDEI specs? It applies from the current spec, but note that TF-A has always generated a new PSTATE (with UAO clear). > > So we can probably drop the clearing of UAO if you prefer. > > I don't like clearing UAO specifically. There may be other PSTATE bits > in the future we don't know or care about and that are left set by > firmware. If we don't trust firmware to give a clean PSTATE, can we > reset it with an ERET? In future we should get the new behaviour, so I think we should be fine there. If we can't trust PSTATE at all, then we're not necessarily able to perform an ERET anyway. ... which I think means I'm arguing in favour of deleting the clearing of UAO, if you're happy with that? Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel